Factors affecting the extent of dermal absorption of solvent vapours: a human volunteer study

We have previously reported that solvent vapours can be absorbed through the skin and that the extent varies markedly and depends on the chemical. For some chemicals, the extent of absorption is significant, e.g. for 1-methoxy-2-propanol dermal absorption accounts for up to 14% of the total absorbed dose after 8 h exposure at the OES. We have conducted a second study using 2-butoxyethanol to investigate the influence of temperature, humidity and clothing on the dermal absorption of vapours. As for the first study, the extent of dermal absorption was determined by biological monitoring to measure the resultant body burden of the chemical.

Four volunteers were exposed on nine occasions. For eight of these exposures they wore air-fed half-masks to supply clean air for the inhalation route. The 'baseline' conditions (one 'whole body' and one 'skin only' exposure) were 25 degrees C, 40% relative humidity with volunteers wearing shorts and T-shirt. For each subsequent exposure, a single parameter was changed: humidity (60%, 65%), temperature (20 degrees C, 30 degrees C) or clothing (minimal and overalls). Finally, a 'industrial scenario' was conducted where volunteers wore overalls over their shorts and T-shirts and environmental conditions reflected high temperature and high humidity (30 degrees C, 60%), such as might be encountered in a tank-cleaning operation or similar.

Results show that 'baseline' dermal absorption of 2-butoxyethanol vapour was, on average, 11% of the total absorbed dose. Higher temperature (30 degrees C, mean 14%, P = 0.03) and greater humidity (65% RH, mean 13%, P = 0.1) increased dermal absorption. The wearing of whole-body overalls did not attenuate absorption (mean 10%). By combining several factors together in the 'industrial scenario', dermal absorption of vapours was significantly increased with a mean of 39% of the total absorbed dose.

The work has shown that dermal absorption of vapours can be significant and that environmental conditions may affect the absorption. Some types of protective clothing may not be suitable to reduce absorption. The possibility of dermal absorption of vapours should be considered particularly for workers in high vapour concentration conditions where control of exposure relies on respiratory protection.